PSI - Issue 22

Yufei Li et al. / Procedia Structural Integrity 22 (2019) 43–50 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Keywords: Premium connection; Sealing ability; Contact pressure; Strength; Thermal cycle; ISO 13679; Finite element analysis

1. Introduction In HPHT (high temperature and high pressure) wells, the requirement for the integrity of premium connections, i.e. connection and sealing ability of connections draws more and more attentions (SY/T 6268 — 2008). Cai et al. (2008) studied that in downhole operation, threaded joints are subjected to multiple loads such as axial force, pressure, bending load and thermal stress, which is the weak link of tubing string connection. Bai et al. (2011) investigate shows that in China, the accidents caused by the failure of threaded joint joints are more than half of the accidents of pipe string failure. Due to structural design defects, traditional API threads are not suitable for complex wells with high difficulty. Cao et al. (2013) studied that premium connections with high connection strength and good sealing performance have been widely used. Xu et al. (2011) advanced Premium connection achieve the purpose of multi-stage sealing mainly through sealing surface and torque shoulder structure. ISO 13679 is widely used for evaluating the ability of tubing and casing connection all over the world (ISO 13679(2002)). Because of the disadvantage of experiment such as long period, high cost and high inquire on the facility. In addition, due to the plastic deformation of connection materials, special thread structure contact load cases of the complexity and diversity, it is difficult to connection sealing integrity problems is described by using analytical solution, considering the economy and convenience of a finite element method, therefore, it is necessary to use finite element numerical simulation software to realize premium connection sealing reliability analysis. Previous studies have provided a good idea for the simulation analysis of the integrity of premium connections (Gabriel et al.(2004), Sugino et al.(2010),). Some assumptions have been made for simplified models, such as ignoring the screw angle, assuming the load on the joints, etc. The influence of temperature effect on the performance of premium connections is seldom analysed in accordance with the test steps of ISO 13679 (Li et al. (2017) Zhang et al. (2016) and Tao et al. (2013)). In order to truly reflect the integrity of premium connections in service environment, a three-dimensional finite element model of a premium connection commonly used in complex wells is established in ABAQUS finite element analysis software. The integrity of the premium connection is simulated and analyzed according to the load applied by ISO 13679 CAL IV series B test and thermal cycle test, which was taken as the basis for measuring its sealing ability. 2. Introduction of premium connection 2.1. Introduction of the structure of premium connection Fig. 1 is a schematic diagram of API threaded joints. There is a certain gap between API meshing threads. Thread grease will evaporate gradually under high temperature and become a leakage channel, which leads to the failure of thread sealing performance. Fig. 2 shows a premium connection which improves the sealing ability of threaded structure. The structures of conical surface and conical surface are adopted. The sealing is realized by the interference fit of the sealing surface and shoulder. The function of threaded part is connecting.

Fig. 1. Schematic diagram of API connection

Fig. 2. Schematic diagram of a premium connection structure.